RISC-V: Stack pointer initialization in crt0

[Kito Cheng]

So the question becomes: what should the sp be initialized to?
__stack_pointer$? the end of the data section? Or another random
address?

This crt0.S is indeed missing some essential initializations, like
`mstatus` and various other CSRs. But, just like Jim Wilson’s view
back then, I also prefer leaving this to the BSP to handle.

On Thu, Jan 2, 2025 at 10:01 PM Christian Herber
<christian.herber@nxp.com> wrote:
>
> Newlib works great when building a linux user space executable.
>
> However, if you want to run something baremetal in M-mode, the standard startup is a roadblock because of the lack of stack pointer initialization.
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> I see there had been discussion on this topic here: https://github.com/riscvarchive/riscv-newlib/issues/39
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> I dislike the current situation as it puts an unnecessary obstacle for users e.g. switching from Arm to RISC-V.
>
> As a user, especially if I build with -spec=nosys.spec, it is strange if the startup assumes an operating system has initialized the stack pointer.
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>
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> This recent reddit thread shows the situation quite well: https://www.reddit.com/r/RISCV/comments/1hjbxyd/running_an_mmode_rv32_cprogram_on_qemu/